1. Field
The following description relates to a scheduling technology, and additionally, to a technology of scheduling a radio resource and a scheduling technology that is applicable to a multi-cell network.
2. Description of Related Art
Recently, interest in a multi-cell network including a plurality of cells has increased. Inter-cell interference may affect throughput of a network in the multi-cell network, and various proposals have been researched to solve inter-cell interference have been performed. Particularly, inter-cell interference usually occurs in outer terminals respectively disposed in outer cells of a plurality of cells.
It is important to efficiently use the radio resource while preventing inter-cell interference from occurring in the outer terminals. As an example, when different radio resources are respectively assigned to outer cells, inter-cell interference rarely occurs in the outer cells. However, in that case, the radio resources may not be effectively used. As an example, when frequency resources F1, F2, and F3 are respectively assigned and fixed to a first outer cell, a second outer cell, and a third outer cell, and a number of outer terminals respectively disposed in the first outer cell, the second outer cell, and the third outer cell is small, the assignment may waste the frequency resources.
Example of Fractional Reuse Method Defined in WiMAX Standard
FIG. 1 is a diagram illustrating a multi-cell network assigning frequency resources to outer cells and inner cells in a related art. Referring to FIG. 1, the multi-cell network includes a plurality of cells 110, 120, and 130, and the plurality of cells 110, 120, and 130 includes base stations BS1, BS2, and BS3, respectively. In this example, each of the plurality of cells 110, 120, and 130 is divided into an inner cell and at least one outer cell based on a distance to a corresponding base station BS1, BS2, or BS3.
In the multi-cell network, interference may occur in outer terminals in outer cells. There may be various methods that may minimize inter-cell interference occurring in the outer terminals, and improve spectral efficiency where a frequency resource usable by the multi-cell network is limited.
It is presumed that total frequency resources usable by the multi-cells network is F1, F2, and F3. In one example, according to the fractional reuse method defined in the WiMAX Standard, to reduce inter-cell interference, the total frequency resource F1+F2+F3 is assigned for each inner cell, and a portion of the total frequency resource is assigned for outer cells. That is, F1 is assigned to an outer cell of the cell 110, F2 is assigned to an outer cell of the cell 120, and F3 is assigned to an outer cell of the cell 130.
According to the fractional reuse method, since each of the inner cells may use all the total frequency resource, a frequency reuse rate of the inner cells may be maximized.
However, since the fractional reuse method does not consider an amount of traffic occurring in the outer cells, quality of service utilized by the outer cells, and a distribution of the outer terminals in the outer cells, the same amount of the frequency resources is fixedly assigned to each of the outer cells. Accordingly, the fractional reuse method may assign, to the outer cells, an excessive amount of the frequency resources when compared with resources utilized, and thereby causing a waste of the frequency resource. In addition, the fractional reuse method may assign an insufficient amount of the frequency resources than a utilized amount of the frequency resources, and thus, a service may not be appropriately provided to the outer terminals.
Also, the inner cells and the outer cells may use a common frequency resource. As an example, the inner cell and outer cell of the cell 110 may commonly use F1. In this example, the inner cell and the outer cell may use F1 at different times, and this may cause a decrease in throughput for all the cells. Particularly, the outer terminal has a relatively lower signal to noise ratio (SNR) as a length of a section of time in which the outer cell uses F1 increases, and thus, the throughput of all the cells may further decrease.
Example of Fractional Reuse Method Defined in IEEE 802.20
FIG. 2 is a diagram illustrating a multi-cell network assigning frequency resources to outer cells and inner cells in another related art. Referring to FIG. 2, according to the fractional reuse method defined in IEEE 802.20, all inner cells in a plurality of cells 210, 220, and 230 use frequency resource F1, and outer cells of the plurality of cells 210, 220 and 230 respectively use frequency resources F2, F3, and F4.
According to the fractional reuse method defined in IEEE 802.20, the frequency resources used by the outer cells and the frequency resource used by the inner cells are different from each other, and thus, although a length of a section of time in which the outer cells use the frequency resources increases, throughput of all the cells may not dramatically decrease because the outer cells and the inner cells use the different frequency resources in the same section of time.
However, the fractional reuse method defined in IEEE 802.20 also assigns fixed frequency resource to each of all the outer cells, and thus, when distribution of outer terminals in the outer cells and an amount of traffic of the outer cells is not considered, like the fractional reuse method, a frequency reuse rate may not increase. Also, since fixed frequency resources are separately assigned for outer cells, there is a burden of determining an optimal amount of frequency resources for the outer cells to maximize efficiency of an entire network.